RO131371B1 - Method for designing shoe lasts for therapeutic footwear, based on biomechanical principles - Google Patents

Description

(54) METHOD OF DESIGNING INsoles FOR THERAPEUTIC FOOTWEAR BASED ON BIOMECHANICAL PRINCIPLES

Examiner, engineer NICOLEANU OCTAVIAN ALEXANDRU lllllllllllllllllllllllllllll^ lllllllllllllllllllllllllllllllll^

Any person has the right to submit, in writing and with reasons, to OSIM, a request for the revocation of the invention patent, within 6 months from the publication of the mention of the decision granting it

RO 131371 Bl

The invention refers to a method of designing cleats for therapeutic footwear based on the biomechanical principles that define the normal functioning of the osteo-musculo-ligamentary system of the foot and intended to obtain the footwear used as an integral part of the treatment of mechanical pathologies of the legs and lower limbs.

Therapeutic footwear has the role of ensuring the modification of the reaction forces acting on the osteo-musculo-ligamentary system so as to favor the healing process of the affected anatomical parts and the efficient functioning of the mechanisms of this system.

The therapeutic action can be exercised both through the constructive elements of the footwear and through the medical devices inserted into the footwear.

The sole is the foundation on which the footwear is designed and made. According to previous practice, the insole is defined as a shape made of various materials and representing the morphology of the foot, being used for the production of footwear.

The socket-foot correspondence is made on the basis of an orthogonal system of axes whose origin is at the rearmost point of the plantar impression of the foot, consisting of: the toe-heel axis located in the transverse plane and passing through the rearmost point of the plantar impression and the tip toe 2, an axis perpendicular to the toe-heel axis and intersecting with it at the extreme posterior point of the plantar surface and located in the transverse plane, and an axis perpendicular to the other two at the origin.

The therapeutic role of footwear has required the redefinition of the shoe so that in its design other principles than morphological ones are also taken into account.

Thus, the sole is a three-dimensional shape modified in relation to the shape of the foot, made of different materials and used in the production of therapeutic footwear, designed based on the anthropometric, morphological, biomechanical, aesthetic and technological information necessary for the footwear to achieve its objectives for which it was prescribed and designed within the conservative treatment of pathologies of the locomotor system.

The plantar surface of the shoe is the support surface for the devices inserted in the shoes. The design and making of the frame can start both from the positive molding of the leg and from the modification of an existing frame, called the initial frame, depending on the size of the deformations of the bone structure of the leg.

The use of CAD-CAM systems allows the flexibility of the production process and the reduction of the delivery time of the final product to the patient. In the case of individualized therapeutic footwear, its prescription parameters are obtained based on the biomechanical examination whose role is to identify both the position of the basic axes of the foot such as the axis of the midtarsal joint or the axis of the subtalar joint as well as the type of foot, based on the relationship between forefoot and hindfoot. The position of the main axes of the foot joints is also evaluated in relation to the initial frame.

A shoe and shoe construction method is known (US 2160991) which consists of designing a shoe as the basis for manufacturing a shoe used to compensate for deficiencies produced by deviations from the normal alignment of the axes and morphology of the foot, by: achieving balance the functions of the leg under load, maintaining posture, preventing excessive pronation, ensuring correct propulsion and reducing the fatigue manifested in the unilateral support phase of walking. In order to fulfill these functions, in the above-mentioned invention, the calapod is modified so as to ensure the control of the calcaneus by tilting the base of the calapod, called the sole of the calapod, to the side, from the posterior area of the calapod to the proximal area of the metatarsophalangeal joints, keeping them in the horizontal plane.

The major disadvantages of this method consist in the fact that with this construction 1 the interior space of the shoe does not allow the insertion of medical devices such as orthoses while the bisector of the posterior part of the shoe is kept vertical and 3 in situations where, due to the existing pathology of the type uncompensated varus or valgus, the calcaneus can no longer achieve such a posture. These deficiencies negatively influence the flexibility of the process of using the shoelace and limit the possibilities of use of the shoes built on its basis. 7

A method of designing shoe soles (US 4597195) is also known to favor the plantarflexion movement of the first metatarsal in the 9th propulsion phase of walking and to facilitate the operation of the pulley mechanism by which the medial band of the plantar aponeurosis wraps around the first joint metatarsophalangeal 11 contributing to the transformation of the leg into a rigid arm and the correct transfer of body weight from one leg to the other. The disadvantage of this method is that the presented invention 13 does not take into account the technical parameters of the sole on which the sole according to the invention will be built, namely the concave shape of the planting surface of the sole. Due to this shape, the 15 metatarsophalangeal joints are positioned in relation to the concave shape of the section of the plantar surface in the corresponding area of the calapod so that the 17 metatarsophalangeal joints 1 and 5 will be positioned higher in relation to the metatarsophalangeal joint 3 compared with all joints resting on a flat surface. In this situation, due to the effect of the arrow of the plantar surface curve of the calapod, the effect induced by the technical solution of the above-mentioned patent can be canceled. 21

There is also a known method of making a shoe with a stiffened sole (118559 B1), applied to the construction of shoes with a heel and whose purpose is to redistribute 23 the pressures between the forefoot and the heel by providing additional support to the rear foot by positioning it as parallel to the surface as possible of support. The disadvantage of this method 25 consists in the fact that it does not take into account the constructive parameters of the frame on which the footwear is formed, respectively the shape of the contour of the longitudinal section of the frame. For example, the above-mentioned invention describes as an essential part a rigid element consisting of a heel cup and an arched part conforming to the lower part of the foot and constructed of plastic material and fixed to the insole by means of an adhesive. Due to the fact that the elements of the intermediate assembly of the shoe (insole, insole reinforcement, glenck) are formed on the shoelace, their shape must be identical to the shape of the contour of the longitudinal section of the shoelace. The non-correlation of the shape of the intermediate assembly of the shoe with the shape of the plantar surface of the sole can lead to the shoe not fulfilling the role for which it was designed. 35

Also known is an orthopedic shoe mold (EP 1516551A2) having a tapered rear section 26 which is sculpted to define a well-fitting rear portion 37 of the shoe. The rear cone has a 25 wide bearing surface and tapers to a narrow elongated neck 27. The forefoot section has a rear to front 39 curve that provides a natural rocker. An orthopedic shoe built on such a form provides stabilization at the heel of the foot and allows an even distribution of pressure in the forefoot 41 .

A shoe mold (US 3496584 A) and a shoe are also known which are improved for a better foot position by asymmetrically curving the heel support surface so that the inner curve rises to a higher level than the 45 outward and extending forward to a point immediately posterior to the balance point, tilting the heel portion outward at the top, and twisting the cone portion 47 so that the top tilts outward aft and inward forward to direct the propulsive forces supporting the weight to the inner region 49 of the balance point.

The technical problem that the invention solves consists in establishing the modifications of the initial shoelace based on biomechanical principles, so that the shoelace for therapeutic footwear obtained leads to a functional product intended for use in the conservative treatment of pathologies of a mechanical nature of the legs and lower limbs.

The design method, according to the invention, removes the disadvantages of the known solutions and solves the mentioned technical problem in that the design stages include one or more of the following processes:

- the realization of a plantar surface of the calapod, without concavity, obtained by sectioning the plantar surface of the initial calapod along a curve parallel to the curve obtained by the intersection of the lateral surface with the plantar surface and located at a distance between 2-5 mm from it and measured to inside the surface. By removing the concave part of the original plantar surface the balance point will be replaced by a balance line;

- torsion of the initial calcaneus in the frontal plane so that the bisector of the posterior surface of the calcaneus is oriented with respect to the support surface at an angle equal to the value of the angle that characterizes the relaxed position of the calcaneus for pathological conditions in which the calcaneus cannot adopt a vertical posture;

- the bending of the initial frame in the transverse plane in relation to the position of the axis of the midtarsal joint determined during the biomechanical examination;

- reduction of tightness in the area of the metatarsophalangeal joint to a minimum value between 1-3 mm and the transfer of this tightness to the proximal area delimited by the metatarsophalangeal joints and the Chopart joint, with values between 3-10 mm. The method, according to the invention, has the following advantages:

- due to the elimination of the concavity of the plantar surface of the socket, the metatarsophalangeal joint 1 rests on a plane located at the same level as the support plane of the metatarsophalangeal joints 2-5, favoring in this way the normal functioning of the pulley mechanism through which the plantar aponeurosis wraps on the distal ends of the metatarsals;

- due to the elimination of the concavity of the plantar surface of the shoe, the medical devices inserted in the shoes will be positioned on a stable surface allowing the achievement of the objectives for which they were prescribed, such as plantarflexion of the first ray or ensuring the necessary range of pronation in the contact phase of the cycle walking, by bending the cleat around the axis of the midtarsal joint relative to the transverse plane, with an angle between +5 and +45 degrees, a physiological relation of the forefoot to the hindfoot in the transverse plane is obtained, thus ensuring comfort increased therapeutic footwear by favoring an improved morphological correspondence of the inner volume of the footwear in relation to the foot;

- by twisting the rear part of the calapod around the mid-tarsal axis relative to the frontal plane, with an angle between -15 and +15 degrees, its alignment with the rear part of the leg is obtained. This alignment is necessary in the case of uncompensated varus/valgus type pathologies in which the rear foot can no longer adopt a vertical posture, by achieving a minimum tightening between 2-5 mm in the area of the metatarsophalangeal joints and a more pronounced tightening between 5 -10 mm in the area delimited by the distal metatarsophalangeal joints and the proximal Chopart joint, favoring the physiological mobility of the metatarsophalangeal joints during the walking cycle, while ensuring an improved stability of the hindfoot and midtarsal joints.

In fig. 1 shows a picture of a standard frame. 1

In fig. 2 shows the section that defines the area of the metatarsal-phalangeal joints, the section in which the perimeter is transposed to the fingers, measured on the foot. Thus, a 3 mold is composed of three surfaces: the upper platform 1, the lateral surface 2 and the plantar surface 3. The upper platform 1 is a flat surface with the role of allowing 5 support in the case of shoe upper forming operations on the mold. The lateral surface 2 is a surface having a complex shape obtained by repeated changes in relation 7 to the corresponding surface of the leg. The plantar surface 3 of the shell is a concave surface characterized by an arrow between 2 and 4 mm in the area of the longitudinal axis 9 of the shell. The arrow is symbolized by s in fig. 2. For aesthetic reasons, the reduction of the perimeter of the socket in the area of the metatarsophalangeal joints in relation to the perimeter 11 of the corresponding section of the leg and the concave shape of the front section of the socket in the same area allow the creation of a supple aspect of the shape at the tip of the socket. From a 13 functional point of view, this perimeter reduction has, traditionally, the role of ensuring the stability of the foot in the footwear by tightening it in the mentioned area. 15

This reduction in perimeter is called tightening and has values between 6-10 mm in the area of the metatarsophalangeal joints and between 2-4 mm in the area between the 17 metatarsophalangeal joints and the area of the Chopart joint. The concave shape of the plantar surface of the cleat determines the existence of a single contact point of the 19 cleat with the support surface in the area of the metatarsal-phalangeal joints, a point called the balance point. The balance point is represented by the number 5 in fig.2. 21

2 examples of the invention are given next

According to an example of the realization of the invention, the method comprises the realization of a functional 23-socket for the pathological condition of hallux limitus made by manual operations:

- select the real initial frame from the frame base. It is chosen both on the basis of traditional dimensional criteria and aesthetic criteria resulting from patient consultation; 27

- modify this formwork according to traditional methods in order to obtain the dimensional correspondence of foot formwork in accordance with the dimensional standards of reference 29;

- the frame is positioned in the fixing system so that the plantar surface is oriented horizontally above the upper platform;

- with respect to the curve resulting from the intersection of the lateral and plantar surfaces of the calapod 33, a curve parallel to it is drawn inwards, at a distance of 3 mm, hereinafter referred to as the boundary curve. This distance is calculated so that the centers of the 35 metatarso-phalangeal joints are positioned on the balance line resulting from the removal of the concave part of the plantar surface; 37

- with the shoe firmly fixed in the position described in point 3, remove the material located on the plantar surface of the shoe and bordered on the outside by the boundary curve 39 described in point 4;

- with the shell thus modified and positioned normally, respectively with the plantar surface 41 facing downwards, check the flatness of contour lines 6, fig. 2, results from the intersection of the front sections of the calapod with the plantar surface; 43

- where the flatness of the contour lines is not achieved, proceed to the rectification of the respective area by adding or removing material until the flatness is obtained.

According to a second embodiment of the invention, the process comprises the creation of a cast for a leg presenting uncompensated valgus of 8 degrees and functional hallux limitus. In this situation, a CAD-CAM system is used:

- the initial virtual box is selected from the database. It is chosen based on both traditional dimensional criteria and aesthetic criteria resulting from patient consultation;

- the frame is changed from a dimensional point of view so that it corresponds to the dimensional standards in force;

- the posterior surface of the calapod corresponding to the hind leg is delimited;

- the position of the midtarsal axis is drawn according to the orientation resulting from the biomechanical examination;

- the posterior part of the calapod is twisted around the direction of the midtarsal axis so that the bisector of the posterior surface is oriented at 8 degrees valgus in the frontal plane. In the situation where the software solution does not have functions that allow such a change, that function is identified that can allow a change as close as possible in the desired sense;

- a smoothing of the intermediate, transitional area between the rear and the front of the frame is carried out;

- the sections of the posterior part are changed, rotated so that the curve resulting from the intersection of the lateral surface of the calapod with the plantar surface is balanced. Balancing means that the points resulting from the intersection of the front sections with the plantar surface are at the same height with respect to the support surface;

- in relation to the curve resulting from the intersection of the lateral and plantar surfaces of the calapod, a curve equidistant from it is drawn inside at a distance of 4 mm from the medial part and 2 mm from the lateral part, hereinafter referred to as the boundary curve. This distance is calculated so that the centers of the metatarsophalangeal joints are positioned on the balance line resulting from the removal of the concave part of the plantar surface;

- the area located on the plantar surface of the calapod and bordered on the outside by the boundary curve described in point 8 is virtually removed;

- a surface bordered on the outside by the boundary curve is created, having as its main characteristic the flatness of contour lines 6, fig.2, resulting from the intersection of the frontal sections of the calapod with the plantar surface;

- the perimeters of the frontal sections are changed so that the tightening falls between 1-3 mm in the area of the metatarsophalangeal joints and between 3-10 mm in the area delimited by the distal metatarsophalangeal joints and the proximal Chopart joint;

- the cast thus designed is virtually compared with the subject's leg;

- if, following the comparison with the leg, it is found that the morphology of the socket corresponds to the prescription, we proceed to the realization of the actual socket using CAM-type technologies. Otherwise, the modification process is repeated until the desired degree of correspondence between the frame and the leg is reached.

Claims (1)

Method of designing the insoles for therapeutic footwear based on 3 biomechanical principles, characterized by the fact that it includes the stages of: - sectioning of the concave part of the planting surface, of the initial frame to be modified 5 at a distance between 2-5 mm from the curve resulting from the intersection of the planting surface with the lateral surface of the frame, measured towards the inside of the planting surface; 7 - torsion of the posterior part of the initial shell around the axis of the midtarsal joint relative to the frontal plane, with an angle between -15 and +15 degrees, so that the bisector of the posterior surface of the shell is oriented with respect to the support surface at an equal angle with the value of the angle that characterizes the relaxed position of the calcaneus in the bilateral orthostatic position, for the pathological conditions in which the calcaneus cannot adopt a vertical position; 13 - bending of the initial calapod in the transverse plane, with an angle between +5 and +45 degrees in relation to the position of the axis of the midtarsal joint determined during the 15th biomechanical examination; - reduction of tightness in the area of the metatarsophalangeal joint to a minimum value 17 in the range of 1-3 mm and the transfer of this tightness in the proximal area delimited by the metatarsophalangeal joints and the Chopart joint, with values between 3-10 mm. 19